diff --git a/contributors.txt b/contributors.txt
index 3d973b8a4..693868d2a 100644
--- a/contributors.txt
+++ b/contributors.txt
@@ -208,6 +208,7 @@ YYYY/MM/DD, github id, Full name, email
 2018/07/03, jgoppert, James Goppert, james.goppert@gmail.com
 2018/07/27, Maksim Novikov, mnovikov.work@gmail.com
 2018/08/03, ENDOH takanao, djmchl@gmail.com
+2018/10/08, xsIceman, Andreas Skaar, andreas.skaar@gmail.com
 2018/10/18, edirgarcia, Edir García Lazo, edirgl@hotmail.com
 2018/07/31, Lucas Henrqiue, lucashenrique580@gmail.com
 2018/08/03, ENDOH takanao, djmchl@gmail.com
@@ -258,4 +259,5 @@ YYYY/MM/DD, github id, Full name, email
 2020/09/06, ArthurSonzogni, Sonzogni Arthur, arthursonzogni@gmail.com
 2020/09/12, Clcanny, Charles Ruan, a837940593@gmail.com
 2020/09/15, rmcgregor1990, Robert McGregor, rmcgregor1990@gmail.com
-2020/09/16, trenki2, Markus Trenkwalder, trenki2[at]gmx[dot]net
\ No newline at end of file
+2020/09/16, trenki2, Markus Trenkwalder, trenki2[at]gmx[dot]net
+2020/10/08, Marti2203, Martin Mirchev, mirchevmartin2203@gmail.com
\ No newline at end of file
diff --git a/doc/cpp-target.md b/doc/cpp-target.md
index 1fc8e8684..edf75f4f6 100644
--- a/doc/cpp-target.md
+++ b/doc/cpp-target.md
@@ -1,6 +1,6 @@
 # C++
 
-The C++ target supports all platforms that can either run MS Visual Studio 2013 (or newer), XCode 7 (or newer) or CMake (C++11 required). All build tools can either create static or dynamic libraries, both as 64bit or 32bit arch. Additionally, XCode can create an iOS library. Also see [Antlr4 for C++ with CMake: A practical example](http://blorente.me//Antlr-,-C++-and-CMake-Wait-what.html).
+The C++ target supports all platforms that can either run MS Visual Studio 2013 (or newer), XCode 7 (or newer) or CMake (C++11 required). All build tools can either create static or dynamic libraries, both as 64bit or 32bit arch. Additionally, XCode can create an iOS library. Also see [Antlr4 for C++ with CMake: A practical example](https://beyondtheloop.dev/Antlr-cpp-cmake/).
 
 ## How to create a C++ lexer or parser?
 This is pretty much the same as creating a Java lexer or parser, except you need to specify the language target, for example:
diff --git a/runtime/CSharp/runtime/CSharp/Antlr4.Runtime/Atn/SingletonPredictionContext.cs b/runtime/CSharp/runtime/CSharp/Antlr4.Runtime/Atn/SingletonPredictionContext.cs
index 2f8f1bb5d..e162dcaca 100644
--- a/runtime/CSharp/runtime/CSharp/Antlr4.Runtime/Atn/SingletonPredictionContext.cs
+++ b/runtime/CSharp/runtime/CSharp/Antlr4.Runtime/Atn/SingletonPredictionContext.cs
@@ -79,7 +79,7 @@ namespace Antlr4.Runtime.Atn
                 return false;
             }
 			Antlr4.Runtime.Atn.SingletonPredictionContext other = (Antlr4.Runtime.Atn.SingletonPredictionContext)o;
-            return returnState == other.returnState && parent.Equals(other.parent);
+            return returnState == other.returnState && (parent != null && parent.Equals(other.parent));
         }
 
 		public override string ToString()
diff --git a/runtime/CSharp/runtime/CSharp/Antlr4.Runtime/Parser.cs b/runtime/CSharp/runtime/CSharp/Antlr4.Runtime/Parser.cs
index b13919923..130e00418 100644
--- a/runtime/CSharp/runtime/CSharp/Antlr4.Runtime/Parser.cs
+++ b/runtime/CSharp/runtime/CSharp/Antlr4.Runtime/Parser.cs
@@ -22,20 +22,20 @@ namespace Antlr4.Runtime
 #if !PORTABLE
         public class TraceListener : IParseTreeListener
         {
-            private readonly TextWriter Output;
 
-            public TraceListener(TextWriter output) {
-                Output = output;
+            public TraceListener(TextWriter output,Parser enclosing) {
+                _output = output;
+                _enclosing = enclosing;
             }
 
             public virtual void EnterEveryRule(ParserRuleContext ctx)
             {
-                Output.WriteLine("enter   " + this._enclosing.RuleNames[ctx.RuleIndex] + ", LT(1)=" + this._enclosing._input.LT(1).Text);
+                _output.WriteLine("enter   " + this._enclosing.RuleNames[ctx.RuleIndex] + ", LT(1)=" + this._enclosing._input.LT(1).Text);
             }
 
             public virtual void ExitEveryRule(ParserRuleContext ctx)
             {
-                Output.WriteLine("exit    " + this._enclosing.RuleNames[ctx.RuleIndex] + ", LT(1)=" + this._enclosing._input.LT(1).Text);
+                _output.WriteLine("exit    " + this._enclosing.RuleNames[ctx.RuleIndex] + ", LT(1)=" + this._enclosing._input.LT(1).Text);
             }
 
             public virtual void VisitErrorNode(IErrorNode node)
@@ -46,15 +46,17 @@ namespace Antlr4.Runtime
             {
                 ParserRuleContext parent = (ParserRuleContext)((IRuleNode)node.Parent).RuleContext;
                 IToken token = node.Symbol;
-                Output.WriteLine("consume " + token + " rule " + this._enclosing.RuleNames[parent.RuleIndex]);
+                _output.WriteLine("consume " + token + " rule " + this._enclosing.RuleNames[parent.RuleIndex]);
             }
 
             internal TraceListener(Parser _enclosing)
             {
                 this._enclosing = _enclosing;
+                _output = Console.Out;
             }
 
             private readonly Parser _enclosing;
+            private readonly TextWriter _output;
         }
 #endif